Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.     

Characterisation of bhringaraj and guduchi herb by ICP-MS analysis, optical absorption, infrared and EPR spectroscopic methods

Leaves of bhringaraj and guduchi herb of Kadapa district of Andhra Pradesh, India, are dried and powdered. ICP-MS analysis of samples indicates that copper is present in both the samples. An EPR study of guduchi sample also confirms the presence of Fe(III) whereas Eclipta alba confirms the presence of Fe(III), Mn(II) and Cu(II). Optical absorption spectrum of guduchi indicates that Cu(II) is present in rhombically distorted octahedral environment. NIR and IR results are due to carbonate fundamentals.     

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

The mechanisms of the reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) are studied. In MALDI mass spectra, ions cationized by copper mostly contain Cu(I) even if Cu(II) salts are added to the sample. It was found that Cu(II) was reduced to Cu(I) by gas-phase charge exchange with matrix molecules, which is a thermodynamically favorable process. Under some conditions, large amounts of free electrons are present in the plume. Cu(II) can be even more efficiently reduced to Cu(I) by free electron capture in the gas phase. The matrices studied in this work are nicotinic acid, dithranol, and 2,5-dihydroxybenzoic acid.     

Two-column ion-exchange method for the determination of copper-complexing capacity and conditional stability constants of copper complexes for ligands in natural waters

Sample solutions titrated with Cu(2+) ions are passed sequentially through two ion-exchange columns in an automated flow system. The first column is packed with Chelex-100 resin and retains Cu(2+) ions that are free or derived from copper complexes that dissociate in the column. The second column is packed with AG MP-1 anion-exchange resin and retains negatively charged Cu(II) complexes. The retained copper species are then eluted from the columns and determined on-line with a flame atomic-absorption spectrophotometer. It is necessary to correct for a small fraction of free Cu(2+) ions that pass through the first column and are retained by the second column. The Cu(II)-complexing capacity of sample solutions is determined from plots of the concentration ratio of free Cu(2+) ions to Cu(II) complexes vs. the concentration of free Cu(2+) ions. Conditional stability constants of the copper complexes are also estimated from these plots. The complexing capacity of sample solutions is also determined rapidly by measuring the concentration of complexed Cu(II) after spiking the sample with an excess of Cu(2+) ions. The sample solutions tested were 4.0muM NTA, 4.0-mg/l. humic acid, and a river water.     

Spectrophotometric determination of a nanomolar amount of ascorbic acid using its catalytic effect on copper(II) porphyrin formation

A simple, fast and sensitive flow-injection method is proposed for the determination of nanomolar amounts of ascorbic acid in tea, urine and blood. The procedure is based on the accelerating effect of a nanomolar level of ascorbic acid on the reaction of cooper(II) with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H(2)tmpyp(4+). Ascorbic acid reduces Cu(II) to Cu(I) which catalyzes the incorporation of Cu(II) into H(2)tmpyp(4+) to form Cu(II)(tmpyp)(4+). In this method two solutions, one containing ascorbic acid and H(2)tmpyp(4+) and the other containing copper(II) and acetate buffer (pH 5.0), were injected into two flowing streams of water through two sample injectors of 120 mu1 sample volume. The mixture was allowed to react in a 2 m reaction coil and the colored solution of Cu(II)(tmpyp)(4+) was monitored at 550 nm (epsilon = 2.01 x 10(4)M(-1)cm(-1)). The present method was applied to the determination of ascorbic acid in tea, urea and blood. Reducing agents such as sugars and vitamins B(1), B(2), B(6) and B(12) did not give serious errors at a concentration of 10(-6) M for the determination of 1.0 x 10(-8)M ascrobic acid. The relative standard deviation of the present method was 2.8% for the determination of 1.0 x 10(-8)M ascorbic acid. The reaction mechanism was clarified from the kinetic results of the formation of Cu(II)(tmpyp)(4+) in the presence of various concentrations of ascorbic acid, copper(II) and hydrogen ion.     

Evaluation of coupled transport across a liquid membrane as an analytical preconcentration technique

When two aqueous solutions are separated by a liquid membrane that contains a complexing agent which is a conjugate base of a weak acid, a metal ion can be transported from the solution of the higher pH against its concentration gradient into the more acidic solution. With Cu(II) as the analyte and a liquid membrane consisting of a mixture of oximes dissolved in kerosene, enrichment factors for a prescribed dialysis time in a simple experimental apparatus were nearly independent of Cu(II) concentration over the range 10(-4)-10(-7)M. With 0.1M hydrochloric acid as the receiver, the enrichment factor was independent of ionic strength and of sample pH in the range 4-9. The effect of sample pH on the interference of Fe(III) was examined. With a pH-2.5 formate buffer, the enrichment factor for Cu(II) decreased as the Fe(III) concentration increased, but in a pH-9.3 ammonium buffer, 0.14 mM Fe(III) did not interfere with the transport of Cu(II) from a 16muM copper sample.     

Voltammetric determination of copper and lead in gasoline using sample preparation as microemulsions.

A voltammetric method for the determination of Cu(II) and Pb(II) in gasoline using sample preparation as three-component solutions (gasoline:propan-1-ol:water, 25:60:15 v/v/v) is proposed. HNO(3) was employed as a supporting electrolyte and to allow the use of aqueous inorganic standards for calibration, even if the analyte species originally in gasoline is present as a metallo-organic form. A square-wave anodic sequential determination was used by measuring the stripping current of Cu(II) (at +104 mV) using a glassy carbon electrode (GCE) and, in a second run, measuring the Pb(II) stripping current (at -470 mV) using a bismuth-film deposited on the surface of the GCE. The method allowed the quantification of 1.7 x 10(-9) mol L(-1) of Cu and 1.4 x 10(-10) mol L(-1) of Pb employing a 1500-s accumulation time. Recovery tests using analyte spiked three-component solutions prepared with commercial gasoline samples enabled recoveries of Cu and Pb from 97 +/- 8 to 102 +/- 5%.     

Cu(II) retention on a humic substance

Humic substances (HS) are macromolecular products derived from a physical, chemical, and microbiological process called "humification." These substances play an important role in the mobility and bioavailability of nutrients and contaminants in the environment. Adsorption isotherms provide a macroscopic view of the retention phenomena. However, complementary techniques are needed in order to study the retention mechanism. The application of the classical models and some modern ones, based on humic substances chemistry, do not accurately describe these adsorption data. The aim of this paper is to model isotherms and combine adsorption data with spectroscopy and microscopy techniques to study the Cu(II) retention on a HS. The adsorption isotherms shape varies significantly with the solution pH from L-type (pH 2-6) to S-type (pH 8). FTIR shows that, when pH is 2 the retention of Cu(II), as [Cu(H(2)O)(6)](2+), is the preferred retention mechanism. The quantity of Cu(II) retained as [Cu(OH)(H(2)O)(6)](+) rises, as pH increases. At pH 4, Cu(II) begins to precipitate, which is the preferred mechanism at pH 8.02. The presence of HS has a great influence on the precipitation process of Cu(II), giving rise to amorphous precipitates. As it is shown by SEM-XRF, Cu(II) distributes heterogeneously on HS surface and accumulates on the humic phases. The presence of different anions (chloride and nitrate) slightly modifies the HS behavior as cation exchanger. When Cl(-) ions are present, part of the Cu(II) form [CuCl(4)](2-), which is stable in solution due to its negative charge; when the anion present is NO(3)(-) the formed complex, [CuNO(3)](+), is retained on the HS.     

Spectrophotometric determination of Cu(II) with sequential injection analysis

A sequential injection system, based on the reaction of Cu(II) with diethyldithiocarbamate (DDTC), was developed for the determination of Cu(II) in plant food and water samples. The extraction procedure, generally used to extract the Cu(II)–DDTC complex for subsequent analysis was eliminated in this procedure. The complex was detected spectrophotometrically in aqueous solutions at 460 nm. The physical and chemical parameters depicting the system were studied to obtain optimum conditions for sample analysis. The system developed is fully computerized and able to monitor Cu(II) in samples at seven samples per hour with a relative standard deviation of <4.50%. The calibration curve is linear from 0.5–5.0 mg/l with a detection limit of 0.2 mg/l. Interferences were reduced by introducing multiple flow reversals, to increase mixing between the reagent and sample zones, and subsequently enhance working of the masking agents (EDTA/citrate).     

Adsorption behavior and mechanism of Cu(II) onto carbonate-substituted hydroxyapatite in the presence of humic acid

In this study, adsorption behavior and mechanism of Cu(II) onto carbonate-substituted hydroxyapatite (CHAP) in the absence and presence of humic acid (HA) were studied in batch experiments. The results showed that carbonate incorporation in HAP could significantly enhance the adsorption of Cu(II). In ternary systems, the presence of HA led to an increase in Cu(II) adsorption, dependent on HA concentration. Kinetic studies showed that pseudo-second-order kinetic model better described the adsorption process of Cu(II) onto CHAP and equilibrium data were best described by Sips models. The order of addition sequences of substrates was found to have a noticeable effect on Cu(II) adsorption onto CHAP. The general trend with respect to Cu(II) adsorption being: (CHAP–Cu)–HA?>?(CHAP–HA)–Cu?>?(Cu–HA)–CHAP. The present findings were important for estimating and optimizing the removal of Cu(II) ions by using CHA as a potential adsorbent.     

Adsorption of Cu(II) and Ni(II) on solid humic acid from the Azraq area, Jordan

Isotherms of adsorption of Cu(II) and Ni(II) onto solid Azraq humic acid (AZHA) were studied at different pH (2.0-3.7) values and 0.1 M NaClO4 ionic strength. The Langmuir monolayer adsorption capacity was found to range from 0.1 to 1.0 mmol metal ion/g AZHA, where Cu(II) has higher adsorptivity than Ni(II). The previously reported NICA-Donnan parameters for sorption of Cu(II) on HA fit the amount of Cu(bound) determined in the present study at pH 3.7 but underestimates those at pH values of 3.0, 2.4, and 2.0. The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may increase the ability of low-affinity sites to encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II). AZHA loaded with Cu(II) and Ni(II) was found to be insoluble in water with no measurable amount of desorbed metal ions.     

Enrichment of copper and nickel with solid phase extraction using multiwalled carbon nanotubes modified with Schiff bases

The behaviour of some Schiff bases in the presence of metal ions is very selective in complex formation. In this study, new, selective and easily prepared adsorbent materials have been developed. Multiwalled carbon nanotubes (MWCNTs) are quite suitable as supporting material for preparation of new solid phase adsorbents modified with Schiff bases due to their selective nature. Different Schiff bases were designed and synthesised as adsorbent agents for Ni(II) and Cu(II) ions, according to the literature, and MWCNTs were modified with these Schiff bases. The modification of CNTs was performed by adsorption from the alcoholic solution of Schiff base. The measurements of Ni(II) and Cu(II) ions were carried out using ICP-MS. Different parameters such as pH, model and eluent solution flow rates, eluent type, amount of ligand, sample volume and effect of foreign ions, which have an effect upon recovery of analytes, were investigated. The obtained results indicated that enrichment can be done with six modified adsorbent materials for Cu(II) at pH 9 and two modified adsorbent materials for Ni(II) at pH 8. It was concluded that four adsorbent materials were selective only for the enrichment of Cu(II). Merely one modified adsorbent material was noneligible for the enrichment of Cu(II) and Ni(II). The solid phase adsorbents prepared by modification with two of the Schiff bases used in this study showed an enrichment factor of 80 for both metal ions, whereas the solid phase adsorbents prepared by modification with four of the Schiff bases showed an enrichment factor of 40 for Cu(II) ions. The confirmation of the developed method was tested with certified reference materials with satisfactory results.     

Mechanisms controlling the cellular accumulation of copper bis(thiosemicarbazonato) complexes

Copper (Cu) bis(thiosemicarbazonato) metal complexes [Cu(II)(btsc)s] have unique tumor-imaging and treatment properties and more recently have revealed potent neuroprotective actions in animal and cell models of neurodegeneration. However, despite the continued development of Cu(II)(btsc)s as potential therapeutics or diagnostic agents, little is known of the mechanisms involved in cell uptake, subcellular trafficking, and efflux of this family of compounds. Because of their high lipophilicity, it has been assumed that cellular accumulation is through passive diffusion, although this has not been analyzed in detail. The role of efflux pathways in cell homeostasis of the complexes is also largely unknown. In the present study, we investigated the cellular accumulation of the Cu(II)(btsc) complexes Cu(II)(gtsm) and Cu(II)(atsm) in human neuronal (M17) and glial (U87MG) cell lines under a range of conditions. Collectively, the data strongly suggested that Cu(II)(gtsm) and Cu(II)(atsm) may be taken into these cells by combined passive and facilitated (protein-carrier-mediated) mechanisms. This was supported by strong temperature-dependent changes to the uptake of the complexes and the influence of the cell surface protein on Cu accumulation. We found no evidence to support a role for copper-transporter 1 in accumulation of the compounds. Importantly, our findings also demonstrated that Cu from both Cu(II)(gtsm) and Cu(II)(atsm) was rapidly effluxed from the cells through active mechanisms. Whether this was in the form of released ionic Cu or as an intact metal complex is not known. However, this finding highlighted the difficulty of trying to determine the uptake mechanism of metal complexes when efflux is occurring concomitantly. These findings are the first detailed exploration of the cellular accumulation mechanisms of Cu(II)(btsc)s. The study delineates strategies to investigate the uptake and efflux mechanisms of metal complexes in cells, while highlighting specific difficulties and challenges that need to be considered before drawing definitive conclusions.     

A cation trap for anodic stripping voltammetry: NH3–plasma treated carbon nanotubes for adsorption and detection of metal ions

NH₃–plasma treated multi-walled carbon nanotubes (pn-MWCNTs) with cation traps for the detection of ultratrace quantities of Zn(II), Cd(II), Cu(II), and Hg(II) using square wave anodic stripping voltammetry (SWASV) is described. The pn-MWCNTs use their adsorption performance to enhance the sensitivity. It is found that under optimized conditions Zn(II), Cd(II), Cu(II) and Hg(II) were individually detected at potentials of −1.16, −0.78, −0.268 and 0.108 V, respectively. The detection limit (3σ method) of 0.314, 0.0272, 0.2263, and 0.1439 nM toward Zn(II), Cd(II), Cu(II), and Hg(II) is achievable, respectively. No interference could be seen during the simultaneous detection of Zn(II), Cd(II), Cu(II), and Hg(II). The pn-MWCNTs exhibit excellent selectivity owing to the different ability of adsorption. A study of the ability of pn-MWCNTs in practical application is carried out using a sample of water collected from Dongpu Reservoir in Hefei City, Anhui, China. It is found that the results were favorable when compared against inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis.     

Determination of Cu(II) and Zn(II) using silica gel loaded with 1-(2-thiasolylazo)-2-naphthol

The silica gel with 1-(2-thiasolylazo)-2-naphthol adsorbed was obtained. The adsorption of Cu(II) and Zn(II) from an aqueous solution onto loaded silica gel was studied. The capabilities of 1-(2-thiasolylazo)-2-naphthol immobilized for Cu(II) and Zn(II) preconcentration, visual and diffusion reflectance spectroscopic detection was evaluated. The detection limits were 10 and 15 microg.l(-1), respectively. Visual test scales for metal ions determination in the range 0.65-13 microg per sample were worked out. The developed methods were applied to Cu(II) and Zn(II) determination in natural and tap water. The obtained results agreed well with the reported value.     

PAS-Formaldehyde Polymer as a Polymeric Ligand

p-Aminosalicylic acid (PAS) was condensed with formaldehyde in the presence of aqueous oxalic acid and aqueous sodium hydroxide. The polymer sample (PAS-F,1) obtained withacid catalyst was characterized by IR spectral study, by its M_n determined by nonaqueous conductometric titration both against standard acid and alkali, by viscometric study in formic acid, and by DTA. The IR spectral and general characteristics of a polymer sample (PAS-F,2) prepared in the presence of aqueous alkali resemble those of a polymer sample (AP-F) prepared similarly from m-aminophenol and formaldehyde, indicating decarboxylation of PAS during the base-catalyzed polymerization of PAS with formaldehyde. Polymeric metal chelates of Fe(III), Cu(II), Zn(II), and Mn(II) ions with the PAS-F,1 polymer sample have been prepared and characterized by elemental analyses, IR spectral study, measurements of magnetic moments, and thermal analyses. Chelation ion-exchanging properties of the PAS-F,1 polymer sample have also been studied employing the batch equilibration method.     

Ion-Pair High-Performance Liquid Chromatographic Retention Behavior of Copper(II)–1-Oxa-4,7,10,13- tetraazacyclopentadecane Complex

The ion-pair high-performance liquid chromatographic retention behavior of copper(II)–1-oxa-4,7,10,13-tetraazacyclopentadecane (Cu(II)–OTACP) complex is discussed with data from indirect spectrophotometric detection on the μBondapak CN column. The mobile phase was acetonitrile solution (MeCN:H₂O 20:80) containing sodium dodecyl sulfate (SDS) as ion-pairing reagent and sodium 1-naphthalenesulfonate (SNS) as detection reagent. The effects of the concentration of SDS and OTACP added to the sample solution to form the Cu(II)–OTACP complex on the capacity factor of the complex, k′, are illustrated. As a consequence of the study, it was found that two peaks anticipated for the 1:1 and 1:2 mole ratio complexes appeared, and the peak anticipated for the 1:2 mole ratio complex could be used to determine the Cu(II) ion. The method has been applied in the determination of Cu(II) ion in waste water and serum.     

Flow-injection potentiometric determination of free cadmium ions with a cadmium ion-selective electrode

The determination of free cadmium ions with solid-state cadmium ion-selective electrode can be performed in non-flow measurements in non-buffered solutions in a wide concentration range down to pCd 10. In cadmium ion buffered solutions linear Nernstian response was obtained even down to pCd 12, which is lower, that expected based on calculation of cadmium solubility from the conditional solubility product. Interferences of trace amounts of Fe(III), Cu(II) and Pb(II) commonly present in natural waters in larger concentrations than Cd(II) can be eliminated by reduction with hydroxylamine, complexation with Neocuproine and ion-exchange on anion-exchange resin in sulphate form, respectively. The developed procedure might be suitable for the determination of activity of free cadmium ions in natural water. A preliminary study on this subject is demonstrated for river water sample using stopped-flow flow-injection system.     

Simultaneous determination of speciation parameters of Cu,Pb, Cd and Zn in model solutions of Suwannee River fulvic acid by pseudopolarography

There is a growing awareness of the importance of quantitative determinations of speciation parameters of the trace metals Cu, Zn, Cd and Pb in aqueous samples containing chemically heterogeneous humic substances, especially when they are present together, interacting with one another and competing for specific binding sites of the humic substances. Such determinations require fundamental knowledge and understanding of these complex interactions, gained through basic laboratory-based studies of well-characterized humic substances in model solutions. Since the chemical heterogeneity of humic substances plays an important role in the thermodynamics (stability) and kinetics (lability) of trace metal competition for humic substances, a metal speciation technique such as pseudopolarography that can reveal the special, distinctive nature of metal complexation is required, and it was therefore used in this study. A comparison of the heterogeneity parameters (Gamma) for Zn(II), Cd(II), Pb(II) and Cu(II) complexes in model solutions of Suwannee River fulvic acid (SRFA) shows that GammaCd>GammaZn>GammaPb>GammaCu, suggesting that SRFA behaves as a relatively homogeneous complexant for Zn(II) and Cd(II), whereas it behaves as a relatively heterogeneous complexant for Pb(II) and an even more heterogeneous complexant for Cu(II) under the experimental conditions used. The order of values of log K* (from the differential equilibrium function, DEF) for the trace metals at pH 5.0 follow the sequence: log K*Cu>log K*Pb>log K*Zn>log K*Cd. These results are in good agreement with the literature values. The results of this work suggest the possibility of simultaneously determining several metals in a sample in a single experiment, and hence in a shorter time than required for multiple experiments.     

Biosorption kinetics, thermodynamics and isosteric heat of sorption of Cu(II) onto Tamarindus indica seed powder

Biosorption of Cu(II) by Tamarindus indica seed powder (TSP) was investigated as a function of temperature in a batch system. The Cu(II) biosorption potential of TSP increased with increasing temperature. The rate of the biosorption process followed pseudo second-order kinetics while the sorption equilibrium data well fitted to the Langmuir and Freundlich isotherm models. The maximum monolayer Cu(II) biosorption capacity increased from 82.97 mg g(-1) at 303 K to 133.24 mg g(-1) at 333 K. Thermodynamic study showed spontaneous and endothermic nature of the sorption process. Isosteric heat of sorption, determined using the Clausius-Clapeyron equation increased with increase in surface loading showing its strong dependence on surface coverage. The biosorbent was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy. The results of FTIR analysis of unloaded and Cu(II)-loaded TSP revealed that -NH(2), -OH, -C=O and C-O functional groups on the biosorbent surface were involved in the biosorption process. The present study suggests that TSP can be used as a potential, alternative, low-cost biosorbent for removal of Cu(II) ions from aqueous media.